Transformer



Sept. 11, 1951 K. G. LAGERLOF TRANSFORMER Filed Dec. 11, 1947 lxvs/z'A/ralf fl MM 631465740, 71%

Patented Sept. 11, 1951 TRANSFORMER Karl G. Lagerlol', Waltham, Mass., assignor to Raytlieon Manufacturing Company, Newton, Masa, a corporation of Delaware Application December 11, 1947, Serial No. 791,021

4 Claims. 1

This invention relates to transformers. and

, more particularly to a laminated shunt assembly for leakage reactance or high-reactance transformers.

Transformers of the aforesaid type generally consist of a main core structure generally rectangular in outline but having one or more openings or windows therein, on which core the primary and secondary windings or coils are wound, and one or more ferromagnetic shunts positioned in the corresponding windows to provide shunt flux paths not linking with one of the coils. As is known, such a transformer is capable of greatly limiting the current, under short-circuit conditions, as compared to the short-circuit current normally produced in a transformer without such shunt or shunts. The short-circuit current in such a shunt or high-reactance transformer depends on and varies with the length of the airgap r non-magnetic gap or gaps between the ferromagnetic shunt and the adjacent portion or portions of the maincore. In order to achieve a predetermined short-circuit current, it is necessary to have a certain predetermined gap length.

It has been found that, with conventional manufacturing techniques, it is very difllcult, in production, to maintain substantially constant, from transformer to transformer, the desired length of gap. In the conventional technique, a plurality of planar laminations are stacked toether to form a shunt assembly, which assembly is then held together by tape or similar means. The assembly is then slipped or forced into place in the window of the main core to provide the aforesaid magnetic shunt.

Thereare several dilliculties involved in this procedure. In the first place, it is very difficult to maintain close tolerances when punching the laminations of the main core and of the shunt iron, and it is diflicult also to maintain the proper close tolerances when lacing or assembling the main core and the shunt assembly. Due to such excessive variations in the dimensions of the main core and of the shunt assembly, the desired airgap varies. Therefore, under these conditions, the short-circuit current will not be within the tolerances allowed, causing rejects with consequent extra labor costs in relacing and retesting.

In addition, in a large percentage of cases it is very difiicult to insert an assembled taped shunt of this type into position, due to slight excesses in size of such shunt assemblies or to slight deficiencies in size of the windows in the main core.

Also, the shunt assembly laminations cannot 2 be held together by taping when the transformer is to be used in oil.

Therefore, an object of this invention is to devise av structure in which one dimension of the shunt assembly is adjustable at the test station, thus enablin the proper short-circuit current to be achieved by adjustment of the shunt airgap to the correct value, without the necessity of maintaining close tolerances in punching and assembling operations, and eliminating extra labor for retaping and retesting.

Another object is to devise a shunt assembly structure which will in all cases slip into place in the main core window very easily.

A further object is to eliminate the necessity of taping together the laminations of the shunt assembly.

A still further object is to devise a structure which will hold the shunt laminations in position more securely, thereby reducing lamination hum,

An additional object is to provide a structure by means of which shunt assemblies may be simply and easily held in place.

Yet another object is to accomplish the above objects in a simple yet effective manner.

The foregoing and other objects of the invention will be best understood from the following description of an exempliflcation thereof, reference being had to the accompanying drawing, wherein:

Fig. 1 is a top or plan view of a single shunt lamination according to this invention, on an enlarged scale;

Fig. 2 is a section on line II-II of Fig. 1;

Fig. 3 is a section on line IIIIII of Fig. 1;

Fig. 4 is an elevation of an assembly or stack of shunt laminations according to the invention, on an enlarged scale;

Fig. 5 is an elevation of a transformer core assembly in which the stack of Fig. 4 may be used;

Fig. 6 is a section on line VIVI of Fig. 5; and

Fig. '7 is a perspective view of the core assembly of Fig. 5, omitting the coils thereof.

Now referring to the drawing, and more particularly to Figs. 1 and 2 thereof, a thin sheet I of ferromagnetic material, for example a suitable iron alloy, is punched out and is bowed during the punching operation or by any other suitable means in such a way that, as shown in Fig. 2, its transverse cross-section is curved and non-planar, or, more specifically, such cross-section is of arcuate shape, with a rather large radius of eurvature, one larger than the maximum face dimension of the sheet. An aperture 2 is punched centrally through the lamination I. Lamination I is bowed, therefore, in contrast to the planar laminations conventionally used, in such a way that it is in the shape of a portion of the lateral wall of a hollow cylinder, and it has one or more apertures 2 therethrough.

Now referring to Fig. 4, in order to form an assembly of laminations for the magnetic shunt of a high-reactance transformer, a plurality of like bowed laminations or sheets I of the type shown in Figs. 1-3 are assembled in stacked or superposed relationship, with the apertures 2 in the several sheets being aligned to provide one or more bores extending through the stack of sheets. For purposes of illustration, ten such sheets are shown as constituting the stack 3 in Fig. 4, but it is to be understood that any other suitable number of sheets may make up the stack half 5 each consisting of approximately the same number of individual sheets. The sheets of upper half 4 are all stacked in such a way that their .centers of curvature are below these sheets. and

the sheets of lower half 5 are all stacked in such a way that their centers of curvature are above these sheets. In this manner, a space 6 is left or provided in the center of the stack 3, the innermost sheet of the upper half 4 and the innermost sheet of the lower half 5 contacting each other at their outer side edges as shown. The several sheets in each of the halves land 5 contact adjacent sheets in the same half throughout substantially their entire areas.

A bolt 1 extends entirely through the stack 3 by means of the aforesaid bore formed by the aligned apertures 2 in sheets I. The head of said bolt engages the outer surface of the top sheet of stack 3, while a nut 8 threaded on bolt 1 engages the outer surface of the bottom sheet of said stack.

At assembly, the stack 3 has a transverse overall dimension a, which is the dimension of said stack when it is not expanded. The sheets I,-

being rather thin, are somewhat flexible. By tightening the nut 8, pressure is obtained and is applied to the stack 3 to press the two halves 4 and 5 thereof together, decreasing the curvature of the sheets or tending to flatten them or make their cross-section planar. In this way, ,the assembly 3 is expanded or has its overall transverse dimension increased to the dimension b. Thus, the transverse dimension of the stack 3 is variable or-adjustable by variation of the pressure exerted thereon by the bolt-and-nut assembly I8.

Due to the firm engagement of the bolt I and nut 8 with the stack 3, and also due to the pressure exerted on said stack by said bolt and nut when the same are tightened, the stack is effectively held together or maintained in assembled relationship by said bolt and nut.

Figs. 5-7 show the application of the assembly .of Fig. 4 to a transformer of the high-reactance type, said assembly being used as a magnetic shunt in such a transformer. Such a transformer may include a laminated main core 9 of magnetic material, for example of the socalled double-E type, having a generally rectangular outer configuration with upper, middle,

and lower spaced horizontal arms or legs I0, II, and I2, respectively. The laminations of core 9 may be clearly seen in Figs. 6 and 7. A primary winding or coil I3 and a secondary coil or winding H are in effect wound on the center arm II and are spaced from each other. An upper space or window I5, throughwhich windings I3 and I4 pass, is provided between central arm II and upper arm l0, and a similar lower space or window I6, through which windings I3 and I4 also pass, is provided between central arm II and lower arm I2.

A magnetic shunt assembly 3 of the type previously described is positioned in window I5 between upper arm II) and central arm II, this assembly being positioned laterally between the two coil windings I3 and I4. As shown in Figs. 6 and '7, assembly 3 has a depth or thickness equal to that of the main core 3, preferably has the same number of laminations as does said main core, and the laminations I of assembly 3 are parallel to the laminations of the main core.

The lower edge of assembly 3 is spaced somewhat above the upper edge of arm II to provide a lower shunt non-magnetic gap and the upper edge of said assembly is spaced-somewhat below the lower edge of arm III to provide an upper shunt non-magnetic gap. The lower gap is provided by a spacer ll of non-magnetic material which has a length equal to the depth of core 9 and assembly 3 and which tightly engages the upper edge of arm II and the lower edge of assembly 3; the upper gap is provided by a similar spacer I8 of non-magnetic material which netic material, such as paper, brass, or aluminum.

A similar magnetic shunt assembly 3A is positioned in window I6 between central arm II and lower arm I2, this assembly being positioned laterally between the two coil windings I3 and I4. In the case of assembly 3A also, upper and lower shunt gaps are provided between the adjacent edges of assembly 3 and core arms II and I2. Spacer IIA of non-magnetic material is positioned in the upper shunt gap between assembly 3A and arm II, while spacer I8A of non-magnetic material is positioned in the lower shunt gap between assembly 3A and arm I2. Shunt assembly 3A is similar to shunt assembly 3, while spacers HA and I3A are similar to spacers l1 and I8, respectively.

Although two gaps are shown in connection with each shunt assembly, it is within the scope of this invention to utilize only one gap in connection with each such assembly, in which case either one of the spacers II or I8 would be ornitted and the shunt assemblies, such as 3, would be placed tightly against either upper arm II or central arm II.,

Also, itis within the scope of this invention to design the main core with only one window rather than two, in which case only one laminated shunt assembly would be used and the windings would be in effect wound on either the upper or lower arm, since in this case there would be no central arm.

In order to hold the assemblies 3 and IA in place in the respective windows I5 and I5, a pair of similar non-metallic bars I9 and 20 are utilized, bar I9 being at the front of the core assembly and bar 20 being at the rear of the assembly.

Bars I9 and 20 may be made of fiber, for example. Bar I3 extends vertically entirely across the fronts of assemblies 3 and 3A and central arm II, and across at least a portion of the front of arms I and I2. Bar I9 is secured to assemblies 3 and 3A by having a pair of appropriatelylocated apertures therein, which are aligned with the bores in the two shunt assemblies and through which the corresonding bolts I extend. Bar 20 extends vertically entirely across the backs of assemblies 3 and 3A and central arm II, and across at least a portion of the back of arms III and I2; bar 20 is secured to assemblies 3 and 3A in the same way as is bar I8, by having a pair of apertures therethrough through which bolts I pass. Thus, it may be seen that the shunt assemblies 3 and 3A are held in place by using bars across the shunt laminations which extend over the main core laminations.

As described previously in connection with Fig. 4, a bow is given to each individual lamination I in order to produce the magnetic shunt assemblies 3 and 3A, and the laminations are stacked with half of the total number of sheets curved in one direction and the other half curved in the opposite direction. In assembling a high-reactance transformer according to this invention, a plurality of bowed laminations I are assembled into a stack to form a shunt assembly with a bolt I and bar I9. This assembly 3 is then inserted into the window I5 of a main transformer core, and bar and nut 8 are threaded into place. Thereafter, at the test bench, the two halves of the shunt assembly 3 are forced together by means of pressure exerted through bolt 8 and nut 1, in the manner previously described, to straighten the shunt laminations I and increase the overall transverse or vertical dimension of the assembly 3, it being remembered that the cross-section of Fig. 2 is taken along a vertical line in Fig. 5. By the above procedure, since the vertical dimension of the shunt assembly is increased by the application of pressure thereto, the spacing between the said assembly and the main core, and therefore also the upper and lower shunt gaps, are decreased. If this adjustment is performed on test, the shunt pile or shunt assembly may be expanded until the correct shunt gaps, and therefore the desired shortcircuit current values, are obtained. The proper short-circuit current is therefore obtained by varying the pressure on the two halves of the shunt lamination assembly, by the pressure exerted by bolts 1 and nuts 8.

It will be seen, from all of the above, that I have devised a structure in which one dimension of the shunt assembly is adjustable at the test station.

The shunt assembly is rigidly held together by bolt 1 and is rigidly held in place, in part, by bolt I and bars I9 and 20. In addition, due to the pressure exerted by bolt I and to the expansion of the shunt laminations into position by deformation thereof, said laminations have a tendency to bite into the spacers I1 and I8 and to bind themselves together rigidly, thus aiding in maintaining them in position and also reducing lamination hum. Taping of the shunt laminations is eliminated.

At assembly of the shunt laminations, before expansion, the assembly has the transverse dimension a which is less than dimension D, the transverse dimension after tightening of the bolt and nut 18. Therefore, the assembly of the transformer is made easier, since on assembly 6 and before tightening on test the length of the shunt assembly is shorter than after tightening, leaving more room in the window into which the shunt assembly is to be inserted for assembly.

Of course, it is to be understood that this invention is not limited to the particular details as described above, as many equivalents will suggest themselves to those skilled in the art. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

What is claimed is:

1. An assembly of laminations for a transformer core, comprising a plurality of thin sheets of ferromagnetic material in stacked relationship, each sheet having a curved non-planar surface, substantially half of the total number of sheets in the assembly being curved in one direction and the other half of the total number being curved in the opposite direction, each sheet having an aperture therethrough and the apertures in the several sheets being aligned to provide a bore extending through the stack of sheets, and means passing through said bore and engaging said sheets for maintaining the sheets in stacked relationship.

2. An assembly of laminations for a transformer core, comprising a plurality of thin sheets of ferromagnetic mtterial in stacked relationship, each sheet having a transverse cross-section of arcuate shape, the stack being divided into lower and upper halves each consisting of approximately the same number of individual sheets, the sheets constituting the lower half of the stack having their centers of curvature thereabove and the sheets constituting the upper half of the stack having their centers of curvature therebelow, whereby a space is provided in the center of the stack and whereby the innermost sheet of the upper half and the innermost sheet of the lower half contact each other at their side edges, and means for pressing the two halves of the stack together to decrease the curvature of the sheets and increase an overall transverse dimension of the assembly.

3. An assembly of laminations for a trans former core, comprising a plurality of thin sheets of ferromagnetic material in stacked relationship, each sheet having a transverse cross-section of arcuate shape, the stack being divided into lower and upper halves each consisting of approximately the same number of individual sheets, the sheets constituting the lower half of the stack having their centers of curvature thereabove and the sheets constituting the upper half of the stack having their centers of curvature therebelow, whereby a space is provided in the center of the stack and whereby the innermost sheet of the upper half and the innermost sheet of the lower half contact each other at their side edges, each sheet having an aperture therethrough and the apertures in the several sheets being aligned to provide a bore extending through the stack of sheets, and means, passing through said bore and engaging the outer surfaces of the top and bottom sheets of the stack, for pressing the two halves of the stack together to decrease the curvature of the sheets and increase the overall transverse dimension of the assembly.

4. A transformer core assembly, comprising a laminated main core having a window therein, a laminated shunt core assembly positioned in said window and providing an airgap between said main core and said assembly, the laminations of .1 said assembly being bowed and extending substantially parallel to the laminations of said main core, means operating on the laminations of said assembly for adjusting said airgap, and means including said last-named means for holding said assembly in position in said window.

KARL G. LAGERLOF.

REFERENCES CITED UNITED s'm'rms PATENTS Number Name Date Eaton Nov. 2, 1915 Fanger July 8, 1941 Hodnette Sept. 24, 1946 Camilli Aug. 17, 1948 Steinmayer Jan. 4, 1949 Sliwiak Feb. 1, 1949 

